1. FIELD OF THE INVENTION
The present invention is generally drawn to reactor tube rib plugs and more particularly to a testing assembly for testing the tube sealing integrity of same.
2. DESCRIPTION OF THE PRIOR ART
In tube-type heat exchangers, a first fluid flows through the tubes of the heat exchanger while a second fluid surrounds the outside of the tubes such that heat exchange occurs between the two fluids. One or more of the tubes can become defective over the life of the heat exchanger such that a leak occurs which allows the two fluids to mingle. When this occurs, it is necessary to plug the tube so that the fluid does not flow through the tube thereby preventing the leakage of the first fluid to the other fluid.
In nuclear reactor power plants, when such a defect occurs in the tubes of a nuclear steam generator the coolant in the tubes is allowed to mingle with the coolant outside of the tubes and a more significant problem arises. A radioactive contamination problem occurs. Since the fluid flowing in the tubes of a nuclear steam generator is generally radioactive, it is important that it not be allowed to leak from the tubes and contaminate the fluid surrounding the tubes. Therefore, when a leak occurs in a nuclear steam generator heat exchange tube, the heat exchange tube is plugged so that the coolant is not permitted to flow through the tube.
One type of tube plug used for the above application is described in U.S. Pat. No. 4,390,042, which patent is incorporated herein by reference thereto. This plug as best seen in FIG. 1 comprises a shell having a tapered inner surface against which an externally tapered expander member moves by application of a pulling force. The motion of the expander member relative to the shell causes the shell to expand into contact with a heat exchange tube thereby plugging the tube. The expander member is formed from a hardened metal with tangentially blended leading radius and a self-locking trailing edge, which provides for ease in expanding the shell while preventing inadvertent unlocking of the plug. The shell has a substantially uniform wall thickness throughout the portion of the shell which experiences expansion so that the force necessary to perform the expanding process does not increase beyond strength limitations of installation equipment as the expander member is moved through the shell. The shell also has a plurality of lands on the outside surface thereof whose depth increases from closed end to open end of the shell so that a substantially uniform wall thickness can be maintained in that region while allowing the lands to contact the inner surface of the heat exchange tube.
The described plug and its position sealing a faulty reactor stem generator tube is best seen in FIG. 2.
However, under certain circumstances these tube plugs may themselves leak either from a faulty installation or from wear over time. Hence, a simple and easy to use testing apparatus was needed to determine the sealing integrity of these tube plugs since it is known that at least one nuclear reactor plant had to come xe2x80x9coff linexe2x80x9d unexpectedly due to primary to secondary leakage beyond allowable limits from the described ribbed tube plugs.
Complex and hard to use integrity testing apparatus are known for testing such ribbed tube plugs. One such system is described in U.S. Pat. No. 5,100,610. This inspection system utilizes an eddy current detector that is rotated to inspect the tube plug. This system is complicated and expensive. There is no teaching in the prior art of a simple, easy to use testing apparatus that uses water injection to pressure test the integrity of the tube plug.
The present invention is drawn to an in-situ pressure testing apparatus for testing the integrity of a rib type seal on a faulty nuclear reactor tube. The apparatus uses a cup-shaped member that seals on the face of the tubesheet containing the faulty tube sealed with the rib plug. The seal is affected by a tubular member of the testing apparatus which sealably extends through the cup-shaped member and which has a mandrel at the end thereof which is threaded into the expander member of the rib plug. When the testing appararus is thus sealed to the tubesheet, pressurized water is admitted to the inside of the testing apparatus and to the rib plug covered by the testing apparatus. The pressurized water is passed through an aperture in the tubular member and through the mandrel into the interior of the rib plug inside the expander member to thus test the integrity of the rib plug seal on both sides of the expander member.
In view of the foregoing it is seen that one aspect of the present invention is to provide a seal integrity testing apparatus for boiler tube seal plugs.
Another aspect of the present invention is to provide a seal integrity testing apparatus for ribbed tube seals used to plug defective boiler tubes in nuclear reactors.
These and other aspects will be more fully understood upon a review of the following description of the preferred embodiment when considered with the accompanying drawings.